Crown rust (Puccinia coronata f. sp. avenae) is the most important disease of oats in Brazil. In susceptible oat cultivars, fungicides are needed to control the disease efficiently. However, spray at low volumes may reduce fungicide performance significantly. A field experiment with the oat cultivar UPFA-20 was carried out at the FAMV/UPF to evaluate the influence of fungicides, rates, and spray volumes on the efficacy of the chemical control for crown rust. The tested treatments combined two fungicides (tebuconazole, Folicur, 0,75 L ha-1; epoxiconazole + pyraclostrobin, Opera, 0,5 L ha-1), four rates (40; 60; 80 and 100% of the commercial rate), and two spray volumes (100 and 200 L ha-1). The field plots were arranged according to a factorial block design (2´4´2) with four replicates. The assessments included the disease severity, disease control, grain quality and grain yield. The net profit of each treatment was also determined based upon the application costs and the sale price of oats at the harvest. At the same rate, for both fungicides, the volume of 200 L ha-1 provided better disease control. At this volume, the 50% rate controlled crown rust as good as the full (100%) rate with 100 L ha-1. The net profit differed between fungicides but not for spray volumes. The rate effects were fungicide dependent.
spray technology; pesticides; economical analysis
